Optical switch and using method therefor

ABSTRACT

Disclosed herein is an optical switch including a plurality of switch cells arranged in the form of an n×n matrix (n is an integer), each switch cell having first and second input ends and first and second output ends, and 2(n−1) reflection cells. The plural switch cells are selectively driven so that one of the first and second input ends of the switch cells in the first column is optically connected to one of the first and second output ends of the switch cells in the n-th column. (n−1) ones of the 2(n−1) reflection cells are arranged so as to optically connect the first output end of the switch cell in the first row, the i-th column (i is an integer satisfying 1≦i≦(n−1)) to the first input end of the switch cell in the first row, the (i+1)-th column. The remaining (n−1) reflection cells are arranged so as to optically connect the second output end of the switch cell in the n-th row, the j-th column (j is an integer satisfying 1≦j≦(n−1)) to the second input end of the switch cell in the n-th row, the (j+1)-th column. This optical switch is suitable for size reduction and can eliminate the path dependence of loss.

This is a Divisional of application Ser. No. 10/340,618, filed Jan. 13,2003, now U.S. Pat. No. 6,748,130.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical switch and a using methodtherefor, and more particularly to an optical switch suitable for a nodein a photonic network using wavelength division multiplexing (WDM).

2. Description of the Related Art

The development and commercialization of a wavelength divisionmultiplexing (WDM) system are proceeding as a communication system thatcan greatly increase a transmission capacity. To construct a large-scalephotonic network by connecting WDM systems, there has been examined aring type or mesh type network obtained by connecting nodes throughoptical fibers in the form of a loop or mesh.

In the ring type network, a transmission capacity in the loop increaseswith an increase in scale of the network. However, in each node, it issufficient to perform processing using a relatively small-scale opticalswitch. To the contrary, in the mesh type network, a transmissioncapacity in each route is small, but it is necessary to performprocessing using a large-scale optical switch in each node.

In a point-to-point link system, an electrical switch is conventionallyused to extract lower-order signals in the node. By substituting anoptical switch for the electrical switch, a cost in the node can bereduced.

Thus, the development of a large-scale optical switch is a keytechnology in constructing various types of networks.

A waveguide type optical switch is known as a conventionalcommercialized small-scale optical switch. The waveguide type opticalswitch includes a switch element and fiber arrays for inputs and outputsconnected to the switch element.

For example, an optical switch referred to as a PILOSS type opticalswitch (Japanese Patent Laid-open No. 63-500140) has been developed toeliminate variations in loss according to the number of switch cellsthrough which light is transmitted. This optical switch is configured byarranging N² switch cells each having two inputs and two outputs at thelattice positions of a matrix with N rows and N columns and suitablyconnecting the inputs and the outputs of the switch cells so as not tocause the path dependence of loss.

As an optical switch which can enlarge an integration scale with a lowloss, there has recently been developed a bubble type optical switchconfigured by forming a bulk at each crossover of crossing type opticalwaveguides and generating a bubble in the bulk to thereby obtain a totalreflection condition. In each switch cell, the transmission and totalreflection of light are switched to thereby obtain a switch functionwith two inputs and two outputs.

On the other hand, a configuration of spatially switching light isconsidered as a traditional technique. By using a reflection mirror asan element for changing an optical path, the problems in performance ofthe waveguide type optical switch, such as on/off ratio and crosstalkcan be almost eliminated. However, such a space switch is large involume, and it is therefore difficult to increase the scale of theswitch from the viewpoint of size.

To break through such circumstances, there has recently been developed atechnique of reducing the size of this space switch by using asemiconductor technology. This technique is referred to as MEMS (MicroElectro Mechanical System), and it is also called optical MEMS in thecase of application to the field of optics.

The optical switch using MEMS has a plurality of small mirrors formed ona substrate by a semiconductor fabrication technique, and performsswitching of optical paths by selectively raising these mirrors bystatic electricity.

Information on MEMS may be provided by IEEE Photonic Technology Letters,Vol. 10, No. 4, April 1998, pp. 525-527.

To increase the scale of a waveguide type optical switch, the yield ofeach switch cell itself formed on the switch element must be increased.However, increasing the yield is relatively difficult because of narrowmanufacturing tolerances. Accordingly, in increasing the scale of thewaveguide type optical switch, it is necessary not only to improve theyield by improving the manufacturing method, but also to remarkablyimprove the performance of the switch element.

In the bubble type optical switch, switching is performed by using theprinciple of total reflection in each switch cell. Accordingly, theangle of crossing of the two optical waveguides connecting the twoinputs and the two outputs in each switch cell is as large as about 90°,causing an increase in switch size. In other words, if the bend radiusof curvature of an optical waveguide connecting the adjacent switchcells arranged on the outermost side is reduced, the loss in thisoptical waveguide is increased. Therefore, the bend radius of curvatureof this optical waveguide must be set to a sufficient amount. Inconnection with this setting, the pitch of the switch cells isdetermined, resulting in an increase in switch size.

In the waveguide type or bubble type optical switch, there is a casethat crossover portions of the waveguides are required on the input andoutput sides, causing an unignorable loss.

Further, in the MEMS type optical switch, there is a possibility thatthe number of reflections on the mirrors may be different according topath in some mode of operation. Accordingly, in the case that thereflection loss by the mirrors is unignorable, there arises a problemthat a path-dependent loss is produced according to a difference innumber of reflections on the mirrors.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an opticalswitch which can be reduced in size.

It is another object of the present invention to provide an opticalswitch which can eliminate the path dependence of loss.

It is a further object of the present invention to provide an opticalswitch which can suppress losses by eliminating crossovers of theoptical waveguides.

Other objects of the present invention will become apparent from thefollowing description.

In accordance with an aspect of the present invention, there is providedan optical switch comprising a plurality of switch cells arranged in theform of an n×n matrix (n is an integer), each of the plurality of switchcells having first and second input ends and first and second outputends; and 2(n−1) reflection cells. The plurality of switch cells areselectively driven so that one of the first and second input ends of theswitch cells in the first column is optically connected to one of thefirst and second output ends of the switch cells in the n-th column.(n−1) ones of the 2(n−1) reflection cells are arranged so as tooptically connect the first output end of the switch cell in the firstrow, the i-th column (i is an integer satisfying 1≦i≦(n−1)) to the firstinput end of the switch cell in the first row, the (i+1)-th column. Theremaining (n−1) reflection cells are arranged so as to optically connectthe second output end of the switch cell in the n-th row, the j-thcolumn (j is an integer satisfying 1≦j≦(n−1)) to the second input end ofthe switch cell in the n-th row, the (j+1)-th column.

With this configuration, the plural reflection cells are provided at thespecific positions with respect to the plural switch cells, so that itis possible to avoid a size enlargement due to an increase in bendradius of curvature as mentioned above and to thereby provide a compactoptical switch.

In accordance with another aspect of the present invention, there isprovided a using method for an optical switch having a plurality ofswitch cells arranged in the form of an n×n matrix (n is an integer),each of the plurality of switch cells having first and second input endsand first and second output ends; and 2(n−1) reflection cells. Theplurality of switch cells are selectively driven so that one of thefirst and second input ends of the switch cells in the first column isoptically connected to one of the first and second output ends of theswitch cells in the n-th column. (n−1) ones of the 2(n−1) reflectioncells are arranged so as to optically connect the first output end ofthe switch cell in the first row, the i-th column (i is an integersatisfying 1≦i≦(n−1)) to the first input end of the switch cell in thefirst row, the (i+1)-th column. The remaining (n−1) reflection cells arearranged so as to optically connect the second output end of the switchcell in the n-th row, the j-th column (j is an integer satisfying1≦j≦(n−1)) to the second input end of the switch cell in the n-th row,the (j+1)-th column. In this method, only the switch cells relating tothe switch cells in the odd-numbered rows, the first column and in theodd-numbered rows, the n-th column or only the switch cells relating tothe switch cells in the even-numbered rows, the first column and in theeven-numbered rows, the n-th column are used.

According to this method, the number of reflections in an optical pathconnecting an arbitrary one of the inputs and an arbitrary one of theoutputs is always 2, and the optical path length of each optical path isconstant irrespective of path, thereby eliminating the production of apath-dependent loss. Further, there are no crossovers at the inputs andthe outputs, thereby eliminating an increase in excess loss.

In accordance with a further aspect of the present invention, there isprovided an optical switch applicable to a first optical fibertransmission line unit and a second optical fiber transmission lineunit. The optical switch comprises a plurality of switch cells arrangedin the form of an n×n matrix (n is an integer), each of the plurality ofswitch cells having first and second input ends and first and secondoutput ends; and 2(n−1) reflection cells. The plurality of switch cellsare selectively driven so that one of the first and second input ends ofthe switch cells in the first column is optically connected to one ofthe first and second output ends of the switch cells in the n-th column.(n−1) ones of the 2(n−1) reflection cells are arranged so as tooptically connect the first output end of the switch cell in the firstrow, the i-th column (i is an integer satisfying 1≦i≦(n−1)) to the firstinput end of the switch cell in the first row, the (i+1)-th column. Theremaining (n−1) reflection cells are arranged so as to optically connectthe second output end of the switch cell in the n-th row, the j-thcolumn (j is an integer satisfying 1≦j≦(n−1)) to the second input end ofthe switch cell in the n-th row, the (j+1)-th column. The second outputend of the switch cell in the first row, the i-th column is opticalconnected to the first input end of the switch cell in the second row,the (i+1)-th column. The first output end of the switch cell in the n-throw, the j-th column is optical connected to the second input end of theswitch cell in the (n−1)-th row, the (j+1)-th column. The first outputend of the switch cell in the k-th row (k is an integer satisfying2≦k≦(n−1)), the i-th column is optically connected to the second inputend of the switch cell in the (k−1)-th row, the (i+1)-th column. Thesecond output end of the switch cell in the k-th row, the i-th column isoptically connected to the first input end of the switch cell in the(k+1)-th row, the (i+1)-th column. The first input ends of the switchcells in the odd-numbered rows, the first column and the second outputends of the switch cells in the odd-numbered rows, the n-th column areinserted in the first optical fiber transmission line unit. The secondinput ends of the switch cells in the even-numbered rows, the firstcolumn and the first output ends of the switch cells in theeven-numbered rows, the n-th column are inserted in the second opticalfiber transmission line unit.

With this configuration, the method according to the present inventionis applicable to bidirectional transmission to thereby obtain an effectthat the switch cells can be efficiently used in addition to theabove-mentioned effect by the method according to the present invention.

In accordance with a still further aspect of the present invention,there is provided an optical switch with N inputs and N outputs (N is aninteger). This optical switch comprises a plurality of switch cellsarranged at the lattice positions of a matrix with n rows (n=2N−1) and(n+1) columns; and two mirrors arranged perpendicularly to a planedefining the matrix and parallel to each other so as to interpose theplurality of switch cells. The number and positions of the plurality ofswitch cells are set so that input paths corresponding to the N inputsand output paths corresponding to the N outputs are parallel to eachother and that the number of reflections in an optical path connectingeach input path and each output path becomes 2.

With this configuration, by arranging N² switch cells at predeterminedones of the lattice positions of the matrix with n (n=2N−1) rows and(n+1) columns, the number of reflections in an optical path connectingan arbitrary one of the inputs and an arbitrary one of the outputs canbe fixed to 2, thereby eliminating the path dependence of loss.

The above and other objects, features and advantages of the presentinvention and the manner of realizing-them will become more apparent,and the invention itself will best be understood from a study of thefollowing description and appended claims with reference to the attacheddrawings showing some preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a first preferred embodiment of theoptical switch according to the present invention;

FIG. 2 is a diagram for illustrating the configuration and operation ofa switch cell;

FIG. 3 is a diagram for illustrating the configuration of a bubble typeswitch cell;

FIG. 4 is a plan view of a PILOSS type optical switch;

FIG. 5 is a plan view for illustrating the drive conditions for eachswitch cell in the first preferred embodiment;

FIG. 6 is a plan view showing a second preferred embodiment of theoptical switch according to the present invention;

FIG. 7 is a table showing the number of reflections in the opticalswitch shown in FIG. 1;

FIG. 8 is a table showing the number of reflections in the opticalswitch shown in FIG. 6;

FIG. 9 is a plan view showing a third preferred embodiment of theoptical switch according to the present invention;

FIG. 10 is a plan view showing a fourth preferred embodiment of theoptical switch according to the present invention;

FIG. 11 is a table showing the number of reflections in the opticalswitch shown in FIG. 9;

FIG. 12 is a table showing the number of reflections in the opticalswitch shown in FIG. 10;

FIG. 13 is a plan view for illustrating a preferred embodiment of theusing method for the optical switch according to the present invention;

FIG. 14 is a plan view for illustrating another preferred embodiment ofthe using method for the optical switch according to the presentinvention;

FIG. 15 is a plan view showing a fifth preferred embodiment of theoptical switch according to the present invention;

FIG. 16 is a diagram for illustrating an example of use of the opticalswitch shown in FIG. 15;

FIG. 17 is a perspective view of a MEMS type optical switch;

FIG. 18 is a plan view showing a sixth preferred embodiment of theoptical switch according to the present invention; and

FIG. 19 is a plan view showing a seventh preferred embodiment of theoptical switch according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Some preferred embodiments of the present invention will now bedescribed in detail with reference to the attached drawings.

FIG. 1 is a plan view showing a first preferred embodiment of theoptical switch according to the present invention. This optical switchis configured by providing a plurality of switch cells SC and aplurality of reflection cells RC on a switch substrate 2 so as toestablish a specific positional relation between these cells SC and RC.Prior to description of this positional relation, the configuration andoperation of each switch cell SC will now be described.

FIG. 2 is a diagram for illustrating the configuration and operation ofeach switch cell SC applicable to the present invention. The switch cellSC has two input ends IN1 and IN2 and two output ends OUT1 and OUT2, andit is electrically driven so as to switch between a bar state where theinput end IN1 and the output end OUT1 are connected and the input endIN2 and the output end OUT2 are connected and a cross state where theinput end IN1 and the output end OUT2 are connected and the input endIN2 and the output end OUT1 are connected.

As the switch cell SC, a conventional waveguide type switch cell may beused and a MEMS type switch cell and a bubble type switch cell to behereinafter described in detail may also be used.

FIG. 3 is a diagram for illustrating the configuration of a bubble typeswitch cell applicable to the present invention. A bulk 4 is formed on asubstrate having optical waveguides for connecting input ends IN1 andIN2 and output ends OUT1 and OUT2. The bulk 4 is filled with a liquid,and the generation of a bubble in the liquid is switched on or off tothereby selectively obtain a reflective state and a transmissive state,which are made to respectively correspond to the bar state and the crossstate. The angle of crossing of the two optical waveguides at acrossover point lying on the bulk 4 is almost 90° to obtain a totalreflection condition.

FIG. 4 is a plan view showing the configuration of a PILOSS type opticalswitch using the bubble type switch cells shown in FIG. 3. In thisexample, 16 switch cells SC are arranged at the lattice positions of a4×4 (4 rows and 4 columns) matrix, so as to obtain an optical switchwith four inputs and four outputs.

In this case, the distance between any two outermost adjacent switchcells SC is √{square root over ( )}2R where R is the radius of curvatureof a curved optical waveguide connecting these two switch cells SC,because the angle of crossing of the two optical waveguides at eachswitch cell SC is almost 90°. Accordingly, in considering the fact thatthe minimum bend radius of curvature of an optical waveguide with nowaveguide loss is several millimeters, it is understood that sizereduction of the optical switch is difficult.

Further, crossovers 8 of the optical waveguides are formed on the inputside and on the output side, causing an unignorable loss.

In the preferred embodiment shown in FIG. 1, an optical switch with fourinputs and four outputs is provided, wherein any arbitrary one of fourinput ports corresponding to four input channels #1 to #4 and anyarbitrary one of four output ports corresponding to four output channels#1 to #4 are selectively connectable with each other. The input channels#1, #2, #3, and #4 are respectively assigned to the input end IN1 of theswitch cell SC in the first row, the first column, the input end IN2 ofthe switch cell SC in the second row, the first column, the input endIN1 of the switch cell SC in the third row, the first column, and theinput end IN2 of the switch cell SC in the fourth row, the first column.The output channels #1, #2, #3, and #4 are respectively assigned to theoutput end OUT2 of the switch cell SC in the first row, the fourthcolumn, the output end OUT1 of the switch cell SC in the second row, thefourth column, the output end OUT2 of the switch cell SC in the thirdrow, the fourth column, and the output end OUT1 of the switch cell SC inthe fourth row, the fourth column.

Further, the input end IN2 of the switch cell SC in the first row, thefirst column, the input end IN1 of the switch cell SC in the second row,the first column, the input end IN2 of the switch cell SC in the thirdrow, the first column, and the input end IN1 of the switch cell SC inthe fourth row, the first column are unused ports. The output end OUT1of the switch cell SC in the first row, the fourth column, the outputend OUT2 of the switch cell SC in the second row, the fourth column, theoutput port OUT1 of the switch cell SC in the third row, the fourthcolumn, and the output end OUT2 of the switch cell SC in the fourth row,the fourth column are also unused ports.

In this preferred embodiment, six reflection cells RC are used to avoidsize enlargement due to the curvature of the curved optical waveguidementioned above with reference to FIG. 4. Three ones of the sixreflection cells RC are arranged so as to connect the output end OUT1 ofthe switch cell SC in the first row, the first column and the input endIN1 of the switch cell SC in the first row, the second column, toconnect the output end OUT1 of the switch cell SC in the first row, thesecond column and the input end IN1 of the switch cell SC in the firstrow, the third column, and to connect the output end OUT1 of the switchcell SC in the first row, the third column and the input end IN1 of theswitch cell SC in the first row, the fourth column. The remaining threereflection cells RC are arranged so as to connect the output end OUT2 ofthe switch cell SC in the fourth row, the first column and the input endIN2 of the switch cell SC in the fourth row, the second column, toconnect the output end OUT2 of the switch cell SC in the fourth row, thesecond column and the input end IN2 of the switch cell SC in the fourthrow, the third column, and to connect the output end OUT2 of the switchcell SC in the fourth row, the third column and the input end IN2 of theswitch cell SC in the fourth row, the fourth column.

While the 4×4 optical switch has been described in this preferredembodiments the connection and arrangement of the switch cells and thereflection cells in the optical switch according to the presentinvention will now be described generally.

To provide an optical switch with n inputs and n outputs (n is aninteger), n² switch cells SC arranged in the form of an n×n matrix and2(n−1) reflection cells RC are used.

(n−1) ones of the 2(n−1) reflection cells RC are arranged so as tooptically connect the output end OUT1 of the switch cell SC in the firstrow, the i-th column (i is an integer satisfying 1≦i≦(n−1)) to the inputend IN1 of the switch cell SC in the first row, the (i+1)-th column.

The remaining (n−1) reflection cells RC are arranged so as to opticallyconnect the output end OUT2 of the switch cell SC in the n-th row, thej-th column (j is an integer satisfying 1≦j≦(n−1)) to the input end IN2of the switch cell SC in the n-th row, the (j+1)-th column.

The output end OUT2 of the switch cell SC in the first row, the i-thcolumn is optically connected to the input end IN1 of the switch cell SCin the second row, the (i+1)-th column.

The output end OUT1 of the switch cell SC in the n-th row, the j-thcolumn is optically connected to the input end IN2 of the switch cell SCin the (n−1)-th row, the (j+1)-th column.

The output end OUT1 of the switch cell SC in the k-th row (k is aninteger satisfying 2≦k≦(n−1)), the i-th column is optically connected tothe input end IN2 of the switch cell SC in the (k−1)-th row, the(i+1)-th column.

The output end OUT2 of the switch cell SC in the k-th row, the i-thcolumn is optically connected to the input end IN1 of the switch cell SCin the (k+1)-th row, the (i+1)-th column.

The input ends IN1 of the switch cells SC in the odd-numbered rows, thefirst column and the input ends IN2 of the switch cells SC in theeven-numbered rows, the first column correspond to input channels #1 to#n of this optical switch.

The output ends OUT2 of the switch cells SC in the odd-numbered rows,the n-th column and the output ends OUT1 of the switch cells SC in theeven-numbered rows, the n-th column correspond to output channels #1 to#n of this optical switch.

This preferred embodiment is based on the assumption that the bar stateand the cross state of each switch cell SC respectively correspond tothe on state and the off state of a switch control signal. Driveconditions for each switch cell SC on this assumption will now bedescribed.

FIG. 5 is a plan view for illustrating the drive conditions for eachswitch cell SC in the preferred embodiment shown in FIG. 1. The numeral(p, q) (p represents the numerals 1 to 4 and q represents the numerals 1to 4) shown in the circle representing each switch cell SC indicates theswitch cell SC switched on when establishing a path between the inputchannel #p and the output channel #q. For example, in the case ofestablishing a path between the input channel #1 and the output channel#1, the control signal for the switch cell SC in the second row, thesecond column is switched on to make a bar state. Accordingly, the inputchannel #1 and the output channel #1 are optically connected with eachother by the reflection in this switch cell SC, the reflection in onereflection cell RC, and the transmission in three switch cells SC. It isapparent that this operation is nonblocking.

According to this preferred embodiment, the distance between any twoadjacent ones of the switch cells SC can be reduced owing to theabove-mentioned arrangement of the reflection cells RC, therebyproviding a compact optical switch.

While each reflection cell RC may be provided by a configuration havingfixed reflecting means unlike each switch cell SC, each reflection cellRC may be replaced by a switch cell SC for the purpose of simplificationof an optical switch manufacturing process. In this case, each switchcell SC placed instead of each reflection cell RC is used always in thebar state, thereby allowing the same operation as that of this preferredembodiment.

FIG. 6 is a plan view showing a second preferred embodiment of theoptical switch according to the present invention. In the firstpreferred embodiment shown in FIG. 1, there are crossovers of theoptical waveguides between the input channels #2 and #3, between theoutput channels #1 and #2, and between the output channels #3 and #4, sothat there is a possibility of increasing of excess loss. To eliminatethis possibility, the second preferred embodiment is improved in settingof the input ports and the output ports and in drive control of theswitch cells SC. The configuration of the second preferred embodimentwill be generally described as an optical switch with n inputs and noutputs as in the above general description of the first preferredembodiment shown in FIG. 1.

Although overlapping the configuration of the first preferred embodimentshown in FIG. 1, a common part of the configuration of the secondpreferred embodiment will first be described.

To provide an optical switch with n inputs and n outputs (n is aninteger), n² switch cells SC arranged in the form of an n×n matrix and2(n−1) reflection cells RC are used.

(n−1) ones of the 2(n−1) reflection cells RC are arranged so as tooptically connect the output end OUT1 of the switch cell SC in the firstrow, the i-th column (i is an integer satisfying 1≦i≦(n−1)) to the inputend IN1 of the switch cell SC in the first row, the (i+1)-th column.

The remaining (n−1) reflection cells RC are arranged so as to opticallyconnect the output end OUT2 of the switch cell SC in the n-th row, thej-th column (j is an integer satisfying 1≦j≦(n−1)) to the input end IN2of the switch cell SC in the n-th row, the (j+1)-th column.

The output end OUT2 of the switch cell SC in the first row, the i-thcolumn is optically connected to the input end IN1 of the switch cell SCin the second row, the (i+1)-th column.

The output end OUT1 of the switch cell SC in the n-th row, the j-thcolumn is optically connected to the input end IN2 of the switch cell SCin the (n−1)-th row, the (j+1)-th column.

The output end OUT1 of the switch cell SC in the k-th row (k is aninteger satisfying 2≦k≦(n−1)), the i-th column is optically connected tothe input end IN2 of the switch cell SC in the (k−1)-th row, the(i+1)-th column.

The output end OUT2 of the switch cell SC in the k-th row, the i-thcolumn is optically connected to the input end IN1 of the switch cell SCin the (k+1)-th row, the (i+1)-th column.

There will now be described a characterized part of the second preferredembodiment shown in FIG. 6 over the first preferred embodiment shown inFIG. 1.

The input ends IN2 of the switch cells SC in the odd-numbered rows, thefirst column and the input ends IN2 of the switch cells SC in theeven-numbered rows, the first column correspond to input channels #1 to#n of this optical switch.

The output ends OUT1 of the switch cells SC in the odd-numbered rows,the n-th column and the output ends OUT1 of the switch cells SC in theeven-numbered rows, the n-th column correspond to output channels #1 to#n of this optical switch.

In the first preferred embodiment shown in FIG. 1, the bar state and thecross state of all the switch cells SC correspond to the on state andthe off state, respectively. In contrast thereto, the condition ofspecific cells is reversed in the second preferred embodiment shown inFIG. 6. More specifically, the bar state and the cross state of theswitch cells SC in the odd-numbered rows, the first column and in theodd-numbered rows, the n-th column correspond to the off state and theon state, respectively, and the bar state and the cross state of theother switch cells SC correspond to the on state and the off state,respectively.

With this configuration, the drive conditions for each switch cell SCdescribed with reference to FIG. 5 can be used as they are, therebyobtaining the effect that a compact optical switch can be provided. Inaddition, it is also possible to obtain an noticeable effect that thecrossovers of the optical waveguides can be eliminated to therebysuppress an increase and variations in excess loss. Furthermore, theoptical waveguides can be easily arranged in parallel at equal intervalsat the input ports and the output ports, thereby obtaining anothereffect that the optical switch can be easily connected to other opticalelements such as optical fiber transmission lines.

FIGS. 7 and 8 are tables showing the numbers of reflections in theoptical paths from the inputs to the outputs in the preferredembodiments shown in FIGS. 1 and 6, respectively. In each of FIGS. 7 and8, the numeral attached to “SW” in each cell indicates the number ofreflections in each switch cell SC, and the numeral attached to “FX” ineach cell indicates the number of reflections in each fixed mirror orreflection cell RC. Further, the numeral shown on the right-hand side ineach cell indicates the total number of reflections in each opticalpath. In the preferred embodiment shown in FIG. 1, the total number ofreflections is classified into three kinds, i.e., 1, 2, and 3 as shownin FIG. 7. In the preferred embodiment shown in FIG. 6, the total numberof reflections is classified into three kinds, i.e., 0, 2, and 4 asshown in FIG. 8.

FIGS. 9 and 10 are plan views showing third and fourth preferredembodiments of the optical switch according to the present invention,respectively. The third preferred embodiment shown in FIG. 9 correspondsto a case where the first preferred embodiment shown in FIG. 1 isexpanded to an optical switch with 8 inputs and 8 outputs, and thefourth preferred embodiment shown in FIG. 10 corresponds to a case wherethe second preferred embodiment shown in FIG. 6 is similarly expanded toan optical switch with 8 inputs and 8 outputs. FIGS. 11 and 12 aretables showing the numbers of reflections in the optical paths frominputs to the outputs in the preferred embodiments shown in FIGS. 9 and10, respectively.

As apparent from FIGS. 11 and 12, the total number of reflections in the8×8 optical switch is similar to that in the 4×4 optical switch. Morespecifically, the total number of reflections in the preferredembodiment shown in FIG. 9 is classified into three kinds, i.e., 1, 2,and 3 as shown in FIG. 11, and the total number of reflections in thepreferred embodiment shown in FIG. 10 is classified into three kinds,i.e., 0, 2, and 4 as shown in FIG. 12.

In the case that the reflection loss is unignorable, there is apossibility of production of path-dependent loss due to the reflectionloss.

In considering the total number of reflections in the preferredembodiment described with reference to FIGS. 9 and 11, it is understoodthat the total number of reflections can be fixed to 2 without thedependence on path by using only the even-numbered channels or only theodd-numbered channels. Accordingly, by using the switch cells SCrelating to the switch cells SC in the odd-numbered rows, the firstcolumn and in the odd-numbered rows, the n-th column or by using theswitch cells SC relating to the switch cells SC in the even-numberedrows, the first column and in the even-numbered rows, the n-th column,the total number of reflections can be fixed to 2 without the dependenceon path, thereby eliminating the path-dependent loss.

FIGS. 13 and 14 are plan views for illustrating different using methodsfor the optical switch according to the preferred embodiment shown inFIG. 9. In the using method shown in FIG. 13, only the switch cells SCrelating to the switch cells SC in the even-numbered rows, the firstcolumn and in the even-numbered rows, the n-th column are used. In theusing method shown in FIG. 14, only the switch cells SC relating to theswitch cells SC in the odd-numbered rows, the first column and in theodd-numbered rows, the n-th column are used. Accordingly, the totalnumber of reflections in the optical switch can be fixed to 2 in such amanner that reflection occurs once in one of the switch cells SC andoccurs once in one of the reflection cells RC in each optical path, thuseliminating the path-dependent loss. According to the using method forthe optical switch according to the present invention, the opticalswitch which can be reduced in size and can suppress an increase inexcess loss can be effectively used with the production of thepath-dependent loss being prevented.

While the using method for the optical switch shown in FIG. 9 has beendescribed to demonstrate the prevention of the production of thepath-dependent loss, the same effect can be obtained also bymanufacturing an optical switch having switch cells SC and reflectioncells RC specifically arranged as shown in FIG. 13 or FIG. 14 and usingthis optical switch.

In the case of using the optical switch shown in FIG. 10 without theproduction of the path-dependent loss, only the switch cells SC relatingto the switch cells SC in the even-numbered rows, the first column andin the even-numbered rows, the n-th column are used.

FIG. 15 is a plan view showing a fifth preferred embodiment of theoptical switch according to the present invention. In this preferredembodiment, the 8×8 optical switch shown in FIG. 9 is effectively usedas two 4×4 optical switches.

FIG. 16 is a block diagram for illustrating an example of use of theoptical switch shown in FIG. 15. Reference numeral 12 denotes theoptical switch shown in FIG. 15. The optical switch 12 has functions oftwo 4×4 optical switches 12A and 12B respectively adapted to upstreamand downstream optical fiber transmission lines 14 and 22. WDM(wavelength division multiplexing) is applied to each of the opticalfiber transmission lines 14 and 22.

The optical fiber transmission line 14 is connected through an opticaldemultiplexer 16 and an optical multiplexer 18 to an optical fibertransmission line unit 20 consisting of a plurality of optical fibertransmission lines, and processing such as routing in the optical fibertransmission line unit 20 is performed by the 4×4 optical switch 12A.Similarly, the optical fiber transmission line 22 is connected throughan optical demultiplexer 24 and an optical multiplexer 26 to an opticalfiber transmission line unit 28 consisting of a plurality of opticalfiber transmission lines, and processing such as routing in the opticalfiber transmission line unit 28 is performed by the 4×4 optical switch12B.

Referring again to FIG. 15 in connection with FIG. 2, the input ends IN1of the switch cells SC in the odd-numbered rows, the first column andthe output ends OUT2 of the switch cells SC in the odd-numbered rows,the n-th column are inserted in the optical fiber transmission line unit20. Further, the input ends IN2 of the switch cells SC in theeven-numbered rows, the first column and the output ends OUT1 of theswitch cells SC in the even-numbered rows, the n-th column are insertedin the optical fiber transmission line unit 28.

Accordingly, the optical switch 12 operates as shown in FIG. 14 for theoptical fiber transmission line unit 20, and operates as shown in FIG.13 for the optical fiber transmission line unit 28, so that a switchingoperation such as routing can be efficiently performed without theproduction of the path-dependent loss. Furthermore, efficientintegration of the switch cells SC can be effected and size reductioncan also be effected by the use of the reflection cells RC, therebyproviding a large-scale and compact optical switch.

There will now be described a configuration capable of eliminating thepath-dependent loss in a MEMS type optical switch.

FIG. 17 is a perspective view of a MEMS type optical switch. Thisoptical switch includes a substrate 32 integrally having 16 switch cellsSC formed by MEMS, mirrors 34 and 36 parallel to each other andperpendicular to a principal surface 32A of the substrate 32, and anoptical unit 38 for providing input paths P1 for input channels (inputports) #1 to #4 and output paths P2 for output channels (output ports)#1 to #4.

The optical unit 38 includes optical fibers 40 provided so as torespectively correspond to the input channels #1 to #4 and opticalfibers 42 provided so as to respectively correspond to the outputchannels #1 to #4. Collimating optical systems are formed by lenses (notshown) between the optical fibers 40 and the optical fibers 42. Theoptical fibers 40 are provided so that the input paths P1 are parallelto each other and inclined relative to the mirrors (reflecting means) 34and 36. The optical fibers 42 are provided so that the output paths P2are parallel to each other and inclined relative to the mirrors 34 and36. In FIG. 17, the optical fibers 40 and 42 are parallel to each otherin the same plane.

The switch cells SC are provided on the principal surface 32A of thesubstrate 32. Each switch cell SC includes a switch mirror 44 movablerelative to the substrate 32, and can switch between a first conditionwhere the switch mirror 44 is parallel to the principal surface 32A anda second condition where the switch mirror 44 is perpendicular to theprincipal surface 32A. In FIG. 17, each switch mirror 44 is parallel tothe mirrors 34 and 36 in the second condition.

Each switch mirror 44 is provided by a small mirror formed on thesubstrate 32 by a semiconductor fabrication technique, and is driven bystatic electricity to thereby switch optical paths.

Since this optical switch employs mirrors, it is superior in switchingperformance to a waveguide type optical switch. Moreover, the switchsize can be reduced to the same level as that of a waveguide typeoptical switch.

FIG. 18 is a plan view showing a sixth preferred embodiment of theoptical switch according to the present invention. In this preferredembodiment, a 4×4 optical switch is provided. Assuming that the pitch ofthe input paths P1 and the output paths P2 is df, the lattice spacing dsin a 4×4 matrix is given as ds=√{square root over ( )}2df.

In this preferred embodiment, a matrix having a lattice spacing of ds/2is assumed, and the positions and number of switch cells SC are set sothat the number of reflections in each optical path from the input tothe output becomes the same number (2). This will now be described moregenerally.

FIG. 19 is a plan view showing a seventh preferred embodiment of theoptical switch according to the present invention. In this preferredembodiment, an N×N optical switch (N is an integer) is provided byexpanding the 4×4 optical switch shown in FIG. 18 for the purpose ofgeneral description.

N² switch cells SC are arranged at the lattice positions of a matrixwith n (n=2N−1) rows and (n+1) columns.

A pair of mirrors 34 and 36 (see FIG. 17) are arranged perpendicularlyto a plane defining the above matrix and parallel to each other so as tointerpose all the switch cells SC.

The number and positions of the switch cells SC are set so that theinput paths P1 corresponding to the N inputs and the output paths P2corresponding to the N outputs are parallel to each other and that thenumber of reflections in an optical path connecting each input path P1and each output path P2 becomes 2. This will now be more specifically.

The N² switch cells SC include a first switch cell group SCG1 consistingof N(N+1)/2 switch cells SC arranged on the input side and a secondswitch cell group SCG2 consisting of N(N−1)/2 switch cells SC arrangedon the output side.

The first switch cell group SCG1 is arranged so as to occupy all thelattice positions included in a region defined by a triangle whose oneside is formed by a line segment including the n lattice points in thefirst column.

The second switch cell group SCG2 is arranged so as to occupy all thelattice positions included in a region defined by a triangle whose oneside is formed by a line segment including the (n−1) lattice points inthe (n+1)-th column.

In regarding the matrix with n rows and (n+1) columns as coordinates,the above arrangement of the switch cells SC may be describedspecifically as follows:

In the first column, at the positions of 1, 3, 5, . . . , and n;

In the second column, at the positions of 2, 4, 6, . . . , and (n−1);

In the third column, at the positions of 3, 5, . . . , and (n−2);

. . .

In the N-th column, at the position of N;

In the (N+2)-th column, at the position of (N−1);

In the (N+3)-th column, at the positions of (N−2) and N;

. . .

In the (n+1)-th column, at the positions of 1, 3, 5, . . . , and (N−2).

According to this preferred embodiment, reflection occurs once in one ofthe switch cells SC and occurs once on the mirror 34 or 36. That is, thetotal number of reflections is always 2, so that the path-dependent losscan be eliminated. Further, an increase in switch size can be suppressedby the half pitch, so that size reduction of the optical switch is nothindered. In addition, the optical path length is also constantregardless of path, and this optical switch can be easily connected toother optical devices because the direction of the input paths P1 is thesame as that of the output paths P2.

According to the present invention as described above, it is possible toprovide an optical switch which can eliminate the path dependence ofloss. It is also possible to provide an optical switch which can bereduced in size. Further, it is possible to provide an optical switchwhich can suppress losses by eliminating crossovers of the opticalwaveguides.

The present invention is not limited to the details of the abovedescribed preferred embodiments. The scope of the invention is definedby the appended claims and all changes and modifications as fall withinthe equivalence of the scope of the claims are therefore to be embracedby the invention.

1. An optical switch with N inputs and N outputs (N is an integer),comprising: a plurality of switch cells arranged at the latticepositions of a matrix with n rows (n=2N−1) and n+1) columns; and twomirrors arranged perpendicularly to a plane defining said matrix andparallel to each other so as to interpose said plurality of switchcells; the number and positions of said plurality of switch cells beingset so that input paths corresponding to said N inputs and output pathscorresponding to said N outputs are parallel to each other and that thenumber of reflections in an optical path connecting each input path andeach output path becomes
 2. 2. An optical switch according to claim 1,wherein the number of said plurality of switch cells is N².
 3. Anoptical switch according to claim 1, wherein said plurality of switchcells comprise a first switch cell group consisting of N(N+1)/2 switchcells arranged on the input side and a second switch cell groupconsisting of N(N−1)/2 switch cells arranged on the output side.
 4. Anoptical switch according to claim 3, wherein: said first switch cellgroup is arranged so as to occupy all the lattice positions included ina region defined by a triangle whose one side is formed by a linesegment including the n lattice points in the first column; and saidsecond switch cell group is arranged so as to occupy all the latticepositions included in a region defined by a triangle whose one side isformed by a line segment including the (n−1) lattice points in the(n+1)-th column.
 5. An optical switch according to claim 1, wherein eachof said plurality of switch cells comprises a switch mirror movablerelative to said plane.
 6. An optical switch according to claim 5,wherein each of said plurality of switch cells switches between a firststate where said switch mirror is parallel to said plane and a secondstate where said switch mirror is perpendicular to said plane.